Russian scientists in the coldest spot on earth have spent a decade drilling down through the ice of Antarctica. They have drilled to a depth of 12,366 feet to reach a freshwater lake the size of Lake Ontario.

Lake Vostok, named after the Russian research station above it, is the largest of more than 280 lakes under the mile-thick ice that covers most of the Antarctic continent. That ice has kept the liquid water of the lake sealed off from light and air for somewhere between 15 million and 34 million years. Vostok is in the middle of the East Antarctic ice sheet about 800 miles from the South Pole.

The lake is believed by some to contain microbes, but that may have been contamination from the drilling fluid. They have studied the lake with radar and other techniques, so they know its shape and location, but what they will learn from water untouched for so many million years is unknown, but enticing. The need to prevent even the slightest contamination is extreme. If life exists in Vostok, it may exist on Europa, one of the moons of Jupiter, which has subsurface icy water. The water in Vostok stays liquid because of the pressure and the warmth of the earth below it.

Next season, American and British expeditions will try to drill to other subterranean lakes.